1. Field of the Invention
The present invention relates to a clutch mechanism to facilitate manual operation of roller doors or shutters which are normally motor driven.
2. Description of the Related Art
Roller doors and shutters are in widespread use in connection with warehouses, factories, garages and many other applications and such roller doors and shutters are typically motor driven by electric motors.
In the event of power failures, fire or other unforseen eventualities the motor driven feature of roller and/or shutter doors may not be operable and it is consequently desirable and indeed mandatory in many applications that manual operation of the doors and/or shutters may be readily achieved independently of the motorised feature. Manual operation of such doors is often achieved by way of an endless chain extending about an overhead chain pulley wheel in turn journalled on an overhead shaft engagable with the shaft about which the roller door or shutter is wound; the chain extending down to an area adjacent ground level whereat it may be pulled by an operator in order to rotate the wheel and shaft and hence the door.
If the chain is to permanently reside on the chain pulley wheel then the chain pulley wheel cannot rotate during ordinary powered operation of the door or shutter having regard to the fact that the high rpm occasioned by motorised operation would cause derailment. It is therefore desirable that a clutch be present in the door mechanism in order that the chain pulley wheel only be engaged with the shaft when the door is to be manually operated.
Various such clutch mechanisms have been proposed to date although most of these are, inconvenient to operate or expensive to manufacture.